1. Field of the Invention
This invention relates to a slider mechanism of a mechanical pencil which can fix a lead guide at positions of its projection and withdrawal.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view showing a prior art slider of a mechanical pencil. In FIG. 1, the slider 20 has a structure in which a lead aperture 21, a sliding member 23 and an elastic body 24 are concentrically configured. A lead guide 12 is fixed at the lead aperture 21, and the lead aperture 21 penetrates through the mechanical pencil along its longitudinal axis direction for passing through a lead 19. The sliding member 23 frictionally slides along the axis direction with an elastic force on the internal peripheral surface 22 of a point member 2. The elastic body 24 holds the lead 19 by elastically engaging it.
The slider 20 moves from the position where the stopper surface 25 of the slider 20 touches the engaging surface 26 of the point member 2 to the position where the rear end of the sliding member 23 touches a lead chuck 4, and the slider 20 brings the lead guide 12 to a projection state and a withdrawal state. The projection state and the withdrawal state of the slider 20 are maintained by means of a small frictional resistance between the sliding member 23 and the internal peripheral surface 22 of the point member 2.
Next, the operation of the prior art slider will be described. When the lead chuck 4 is pushed out through a lead pipe 3 by a knocking operation of a rear end knock portion (not shown) of the mechanical pencil, the chuck fastening ring 7 first stops against the end portion 27 of the point member 2 while the lead chuck 4 continues to move, to thereby unfasten the lead chuck 4 so as to release the lead 19 from the chuck 4, then the front end of the lead chuck 4 touches the slider 20 and pushes it to project the lead guide 12 out by moving the slider 20 to the position where the stopper surface 25 touches the engaging surface 26. After that, if the knocking operation is removed, the lead chuck 4 returns to its original position through the repulsive force of the elastic body 9, and the chuck fastening ring 7 then fastens the lead chuck 4 to fix the lead 19. The lead 19 is sent out from the tip portion of the lead guide 12 by repeating the aforementioned operation. Thus, the lead guide 12 projects from the point member 2 in a slider type mechanical pencil, contrary to a fixed type mechanical pencil (not shown), where the lead guide is always kept in the projection state because the slider portion is constructed together with the point member in the pencil body.
After writing, the lead 19 is in a state in which the lead 19 is fastened by the lead chuck 4. From this state, when the rear end knock portion is knocked while also pushing the tip portion of the lead guide 12 with an appropriate means such as the tip of a finger and the like, the lead 19 is released from the fastening of the lead chuck 4 and it is moved to the right in FIG. 1 by the pushing force, then the lead 19 withdraws into the point member 2 together with the lead guide 12.
Because the prior art slider is configured as remarked above, it has the following problem. That is to say, when the prior art mechanical pencil is used with a ruler, the lead guide 12 often withdraws by itself if it contacts the ruler, and the lead 19 is left exposed. That is to say, the lead 19 is left in a projection state, and it will be easily broken.
The aforementioned fixed type mechanical pencil, namely the popular and ordinary mechanical pencil whose lead guide 12 is fixed to the point member 2, has such a problem that the tip of the always projecting lead guide 12, even if the pencil is not used, will often injure clothes or persons.